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| United States Patent |
5,585,459
|
|
Tanaka
, et al.
|
December 17, 1996
|
Process for producing raw rubber
Abstract
A process for producing raw rubber from a deproteinized natural rubber is
disclosed, which comprises coagulating rubber particles in the
deproteinized natural rubber latex by: (1) adding a nonionic surfactant
having a cloud point of from 20.degree. to 100.degree. C. and a molecular
weight of 300 or more to the deproteinized natural rubber latex and
heating the latex to a temperature not lower than the cloud point of the
nonionic surfactant; or (2) adding a coagulation assistant selected from
the group consisting of: (a) an anionic surfactant, (b) an amphoteric
surfactant, (c) a nonionic surfactant, (d) a nonionic or amphoteric
oligomer or polymer, and (e) an anionic oligomer or polymer, to the
deproteinized natural rubber latex; and then recovering the coagulated
rubber particles. According to the process of the present invention, raw
rubber containing substantially no metal ion can be produced with a high
efficiency.
| Inventors:
|
Tanaka; Yasuyuki (Tokyo, JP);
Hioki; Yuichi (Wakayama, JP);
Hayashi; Masaharu (Wakayama, JP);
Ichikawa; Naoya (Hyogo, JP);
Sakaki; Toshiaki (Hyogo, JP)
|
| Assignee:
|
Kao Corporation (Tokyo, JP);
Sumitomo Rubber Industries, Ltd. (Hyogo, JP)
|
| Appl. No.:
|
241714 |
| Filed:
|
May 12, 1994 |
Foreign Application Priority Data
| May 13, 1993[JP] | 5-111766 |
| May 13, 1993[JP] | 5-111767 |
| Current U.S. Class: |
528/486; 524/376; 524/498; 524/575.5; 528/1; 528/488; 528/489; 528/491; 528/502R |
| Intern'l Class: |
C08C 001/14; C08C 001/15; C08C 001/04 |
| Field of Search: |
528/487,486,488,502,1,931,934,932
524/376,498,903,925,929
|
References Cited
U.S. Patent Documents
| 2061276 | Nov., 1936 | Ingmanson | 528/932.
|
| 2097481 | Nov., 1937 | Wallerstein | 528/932.
|
| 2399156 | Apr., 1946 | Stamberger et al. | 528/932.
|
| 3761455 | Sep., 1973 | Tanaka et al. | 528/488.
|
| 4379095 | Apr., 1983 | Oldack | 524/376.
|
| 4455265 | Jun., 1984 | Haldeman | 524/925.
|
| Foreign Patent Documents |
| 309245 | Apr., 1929 | GB.
| |
| 1192407 | May., 1970 | GB.
| |
| 2098222 | Nov., 1982 | GB.
| |
Primary Examiner: Michl; Paul R.
Assistant Examiner: Asinovsky; Olga
Attorney, Agent or Firm: Sughrue, Mion, Zinn, Macpeak & Seas
Claims
What is claimed is:
1. A process for producing raw rubber which comprises coagulating rubber
particles in a deproteinized natural rubber latex by adding a nonionic
surfactant having a cloud point of from 20.degree. to 100.degree. C. and a
weight average molecular weight of 300 or more to the deproteinized
natural rubber latex and heating the latex to a temperature not lower than
the cloud point of the nonionic surfactant.
2. The process of claim 1, wherein said nonionic surfactant having a cloud
point of from 20.degree. to 100.degree. C. and a molecular weight of 300
or more is added in an amount of from 0.01 to 10% by weight based on the
solids content of the deproteinized natural rubber latex.
Description
FIELD OF THE INVENTION
The present invention relates to a process for producing raw rubber. More
particularly, the present invention relates to a process for producing raw
rubber comprising coagulating rubber particles in a deproteinized natural
rubber latex.
BACKGROUND OF THE INVENTION
Natural rubber has hitherto been used widely as industrial products, such
as automobile tires, belts and pressure-sensitive adhesives, and household
goods, such as gloves. These natural rubber articles are generally
produced by coagulating the rubber content of a natural rubber latex to
obtain raw rubber called crepe rubber or smoked sheet rubber, and further
processing the raw rubber through steps of mastication, compounding of
additives, molding, and vulcanization.
It was recently reported that medical tools made of natural rubber, such as
surgical gloves, various catheters, and analgesic masks, provoke labored
respiration or anaphylactoid symptoms, such as vascular edema, nettle
rash, detelectasis and cyanosis, in patients. Cases were also reported in
which women with a history of allergy suffered a pain in the hands, nettle
rash or vascular edema around the eyes when they used rubber gloves made
of natural rubber.
These symptoms seem to be attributed to the protein present in natural
rubber. Food and Drug Administration (FDA), U.S.A. has called on
manufactures of natural rubber to reduce the protein content. It has
therefore been demanded to remove protein from natural rubber.
Natural rubber is obtained from Hevea trees as a latex containing a rubber
content, water, protein, inorganic salts, and other impurities. The latex
oozing out from the tapped trunk of a rubber plant is collected in a cup,
gathered at a refining factory where it is coagulated to obtain raw rubber
(crepe rubber or smoked sheet rubber) or concentrated by centrifugation to
obtain a purified latex.
The protein content in natural rubber has usually been expressed in terms
of a nitrogen content (N %) determined by a Kjeldahl method multiplied by
6.3. The present inventors discovered that the proteins in raw rubber
obtained from a latex can be confirmed by infrared absorption at 3280
cm.sup.-1 characteristic of polypeptide.
The present inventors previously found that a deproteinized natural rubber
latex showing no IR absorption at 3280 cm.sup.-1 can be obtained by a
process comprising treating a natural rubber latex with a protease and a
surfactant either simultaneously or successively and, after allowing the
system to stand for a given period of time, recovering the rubber
particles by centrifugation (see Japanese Patent Application Nos. 208754
to 208758/92 (corresponding to EP-A-0 584 597)).
As a method for recovering the rubber particles from natural rubber latex,
a method comprising adding an acid (e.g., formic acid and acetic acid) to
a latex and a method comprising adding an inorganic salt (e.g., calcium
chloride, aluminum sulfate and calcium nitrate) are generally known.
For example, a latex is diluted to have a solids content of about 15 to 20%
by weight, and formic acid is subsequently added thereto in a
concentration of from 0.1 to 1% by weight to agglomerate the rubber
particles, which is then separated, washed and dried to recover it.
As compared with the general latex on the market, the above-mentioned
deproteinized latex is very poor in the mechanical stability. However, in
contrast, when it is attempted to recover the rubber content in the
deproteinized latex by addition of an acid, the deproteinized latex causes
only insufficient agglomeration to recover the rubber content. On the
other hand, when the above-mentioned method wherein an inorganic salt is
added to undergo agglomeration is employed, metal ions are unavoidably
incorporated into the resulting solid rubber, which causes problems such
as reductions in physical properties due to moisture absorption, blooming,
retardation of vulcanization, and a reduction in resistance to
deterioration on aging.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for producing
raw rubber from a deproteinized natural rubber latex with a high
efficiency.
Another object of the present invention is to provide a process for
producing raw rubber from a deproteinized natural rubber latex without
incorporating metallic ions into the raw rubber.
As a result of extensive investigation, the present inventors have found
that raw rubber containing no metal ions can be produced from a
deproteinized natural rubber latex with high efficiency by adding a
specific nonionic surfactant to the latex and then heating the resulting
latex, or by adding a specific surfactant or a specific oligomer or
polymer to the latex and further adding thereto an acid, such as formic
acid or acetic acid.
Namely, the present invention provides a process for producing raw rubber
which comprises coagulating rubber particles in a deproteinized natural
rubber latex by:
(1) adding a nonionic surfactant having a cloud point of from 20.degree. to
100.degree. C. and a molecular weight of 300 or more to the deproteinized
natural rubber latex and heating the latex to a temperature not lower than
the cloud point of the nonionic surfactant; or
(2) adding a coagulation assistant selected from the group consisting of:
(a) an anionic surfactant,
(b) an amphoteric surfactant,
(c) a nonionic surfactant,
(d) a nonionic or amphoteric oligomer or polymer, and
(e) an anionic oligomer or polymer to the deproteinized natural rubber
latex; and then recovering the coagulated rubber particles.
DETAILED DESCRIPTION OF THE INVENTION
The nonionic surfactant which can be used as a coagulating agent in the
step (1) of the process of the present invention has a cloud point of from
20.degree. to 100.degree. C. and a molecular weight of 300 or more,
preferably a cloud point of from 20.degree. to 100.degree. C. and a
molecular weight of 1,000 or more, more preferably a cloud point of from
20.degree. to 80.degree. C. and a molecular weight of 1,000 or more.
A nonionic surfactant having a cloud point of less than 20.degree. C. is
difficult to handle at room temperature, while a nonionic surfactant
having a cloud point exceeding 100.degree. C. is difficult to exhibit
coagulating effect to the deproteinized natural rubber latex. On the other
hand, a nonionic surfactant whose molecular weight is less than 300 is
difficult to efficiently coagulate the rubber content. The molecular
weight of the nonionic surfactant as referred herein is an average
molecular weight. The average molecular weight of the copolymer and
condensate nonionic surfactants can be determined, for example, by
analysis with an aqueous GPC (liquid chromatography) using sodium
polystyrenesulfonate as standard, while the average molecular weight of
the nonionic surfactant other than the copolymer and the condensate can be
determined, for example, by the measurement of its hydroxyl group value
and calculation based on the molecular weight of KOH.
Specific examples of the nonionic surfactant as the coagulating agent
include polyoxyalkylene ethers, organopolysiloxane-polyoxyalkylene
copolymers, polyoxyalkylene adducts of a formalin condensate of phenol or
an alkylphenol, and polyoxyalkylene adducts of bisphenol A or bisphenol S.
The nonionic surfactant is preferably used in an amount of from 0.01 to 10%
by weight, more preferably from 0.1 to 5% by weight, based on the solids
content of the deproteinized natural rubber latex. If the amount is less
than 0.01% by weight, the coagulating effect is insufficient. On the other
hand, if the amount exceeds 10% by weight, it is uneconomical and the
content of the surfactant remaining in the resulting raw rubber increases.
The nonionic surfactant which can be used in the present invention includes
polyoxyalkylene esters, polyoxyalkylene ethers, polyoxyalkylene polyhydric
alcohol esters, polyoxyalkylene sugar fatty acid esters,
organopolysiloxane-polyoxyalkylene copolymers, polyoxyalkylene adducts of
phenol- or alkylphenol-formalin condensates, and polyoxyalkylene adducts
of bisphenol A or S.
Examples of the polyoxyalkylene group in the above-illustrated nonionic
surfactants include those having an alkylene group containing 2 to 4
carbon atoms. The number of added moles of ethylene oxide, for example, is
from about 1 to about 300, preferably from about 5 to about 300.
These nonionic surfactants may be used either individually or in
combination of two or more thereof selected appropriately.
The nonionic surfactant may be added to the latex immediately after
deproteinizing process of the natural rubber latex or before the
deproteinizing process of the natural rubber latex. In general, it is
preferred that the nonionic surfactant is added to the latex after
deproteinizing process of the natural rubber latex.
In the coagulation step (1) in the process of the present invention, a
deproteinized natural rubber latex containing the nonionic surfactant as a
coagulating agent is heated to a temperature not lower than the cloud
point of the nonionic surfactant. The order of the addition of the
coagulating agent (the nonionic surfactant) and the heating is not
limited, and the latex may previously be heated before addition of the
coagulating agent, or addition of the coagulating agent may be followed by
heating.
The coagulation assistant which can be used in the step (2) of the process
of the present invention is explained below in detail.
The anionic surfactant as coagulation assistant (a) includes carboxylic
acid surfactants, sulfonic acid surfactants, sulfuric ester surfactants
and phosphoric ester surfactants.
Examples of the carboxylic acid surfactant include fatty acid salts
containing from 6 to 30 carbon atoms, polycarboxylic acid salts,
rosinates, dimer acid salts, and tall oil fatty acid salts, with
carboxylic acid salts containing from 10 to 30 carbon atoms being
preferred. Those having more than 30 carbon atoms tend to be difficult to
disperse in water. Preferred examples of the polycarboxylic acid include
straight-chain or aromatic, saturated or unsaturated dicarboxylic and
tricarboxylic acid which may be substituted by hydroxy, amino, ketone
group, such as citric acid, ketoglutaric acid, succinic acid, fumaric
acid, maleic acid, malic glutamic acid, asparagic acid, phthalic acid,
trimellitic acid and pyromellitic acid.
Examples of the sulfonic acid surfactant include alkylbenzenesulfonates,
alkylsulfonates, alkylnaphthalenesulfonates, naphthalenesulfonates,
diphenyl ether sulfonates, .alpha.-olefin sulfonates, dialkyl
sulfosuccinates, .alpha.-sulfonated fatty acid salts, and methyloleyl
taurine. Among them, alkylbenzenesulfonates, alkylnaphthalenesulfonates
and dialkylsulfosuccinates wherein the alkyl moiety has from 6 to 30
carbon atoms, preferably from 8 to 20 carbon atoms.
Examples of the sulfuric ester surfactant include alkylsulfuric ester
salts, polyoxyalkylene alkylsulfuric ester salts, polyoxyalkylene
alkylphenyl ether sulfuric ester salts, polyoxyalkylene tristyrenated
phenol sulfuric ester salts, and polyoxyalkylene distyrenated phenol
sulfuric ester salts. Among them, alkylsulfuric ester salts,
polyoxyalkylene alkylsulfuric ester salts, polyoxyalkylene alkylphenyl
ether sulfuric ester salts, and polyoxyalkylene distyrenated phenol
sulfuric ester salts. Examples of the polyoxyalkylene group include those
comprising from 1 to 100 mol, preferably from 1 to 50 mol, of an alkylene
oxide having 2 to 4 carbon atoms, preferably from 2 to 3 carbon atoms.
Examples of the alkyl group include those having 6 to 30 carbon atoms,
preferably from 8 to 20 carbon atoms.
Examples of the phosphoric ester surfactant include alkyl phosphoric ester
salts and polyoxyalkylene phosphoric ester salts. Preferred examples
thereof include alkyl phosphoric ester salts wherein the alkyl moiety has
from 8 to 20 carbon atoms, and polyoxyalkylene phosphoric ester salts
wherein the polyoxyalkylene moiety comprises from 1 to 100 mol, preferably
from 1 to 50 mol, of an alkylene oxide having from 2 to 3 carbon atoms.
The salts of these compounds as coagulation assistant (a) include salts
with a metal (e.g., Na, K, Ca, Mg or Zn), ammonia salts, and amine salts
(e.g., triethanolamine salt).
The amphoteric surfactant as coagulation assistant (b) includes amino acid
surfactants, betaine surfactants, and amine oxide surfactants.
Preferred examples of the amino acid surfactant include
monoalkylaminoalkylene carboxylic acid salts and dialkylaminoalkylene
carboxylic acid salts.
Preferred examples of the betaine surfactant include
alkyldimethylcarboxymethylammonium betaines, trialkylsulfoalkyleneammonium
betaines, dialkylbispolyoxyalkyleneammonium sulfuric ester betaines,
alkylcarboxymethylhydroxyethylimidazolinium betaines. Among them,
alkyldimethylcarboxymethylammonium betaines are more preferred.
Preferred examples of the amine oxide surfactant include alkyldimethylamine
oxides.
In the above-mentioned amphoteric surfactants, examples of the alkyl group
include an alkyl group containing from 6 to 30 carbon atoms, preferably
from 8 to 20 carbon atoms, and more preferably from 10 to 16 carbon atoms.
The nonionic surfactant as coagulation assistant (c) includes
polyoxyalkylene ether surfactants, polyoxyalkylene ester surfactants,
polyhydric alcohol fatty acid ester surfactants, sugar fatty acid
surfactants, and alkyl polyglucoside surfactants.
Examples of the polyoxyalkylene ether surfactant include polyoxyalkylene
alkyl ethers, polyoxyalkylene alkylphenyl ethers, polyoxyalkylene polyol
alkyl ethers, polyoxyalkylene styrenated phenol ethers, and
polyoxyalkylene tristyrenated phenol ethers. Examples of the polyol of the
polyoxyalkylene polyol alkyl ethers include polyhydric alcohols having 2
to 12 carbon atoms, such as propylene glycol, glycerin, sorbitol, glucose,
sucrose, pentaerythritol, and sorbitan. Among them, polyoxyalkylene alkyl
ethers and polyoxyalkylene alkylphenyl ethers are preferred.
Examples of the polyoxyalkylene ester include polyoxyalkylene fatty acid
esters.
Examples of the polyhydric alcohol fatty acid ester include fatty acid
esters of a polyhydric alcohol containing 2 to 12 carbon atoms and fatty
acid esters of a polyoxyalkylene polyhydric alcohol. Specific examples
thereof include a sorbitol fatty acid ester, a sorbitan fatty acid ester,
a fatty acid monoglyceride, a fatty acid diglyceride, and a polyglycerin
fatty acid ester. Polyalkylene oxide adducts of these ester compounds,
such as a polyoxyalkylene sorbitan fatty acid ester and a polyoxyalkylene
glycerin fatty acid ester, may also be used. Among them, fatty acid esters
of a polyhydric alcohol is preferred. More specific examples thereof
include polyoxyalkylene sorbitol fatty acid esters, polyoxyalkylene
sorbitan fatty acid esters, polyoxyalkylene glycerin fatty acid esters and
polyglycerin fatty acid esters.
Examples of the sugar fatty acid ester include a fatty acid ester of
sucrose, glucose, maltose, fructose or a polysaccharide. A polyalkylene
oxide adduct of these esters may also be used. Among them, a fatty acid
ester of sucrose is preferred.
Examples of the alkyl polyglucoside include an alkylglucoside and an alkyl
polyglucoside. Fatty acid esters of these compounds may also be used.
Polyalkylene oxide adducts of these compounds are also employable. Among
them, an alkyl polyglucoside and a polyoxyalkylene oxide adduct of an
alkylglucoside are preferred.
In the above-mentioned nonionic surfactants, examples of the alkyl group
include an alkyl group containing from 4 to 30 carbon atoms. The
polyoxyalkylene group includes those having an alkylene group containing
from 2 to 4 carbon atoms. The number of moles of an added alkylene oxide,
e.g., ethylene oxide, is from about 1 to 50. The fatty acid includes
straight-chain or branched and saturated or unsaturated fatty acids
containing from 4 to 30 carbon atoms.
The nonionic or amphoteric oligomer or polymer as coagulation assistant (d)
includes polyvinyl alcohol, polyethylene glycol, ethylene oxide-propylene
oxide copolymers, hydroxyethyl cellulose, hydroxypropyl cellulose, methyl
cellulose, and starch derivatives.
The anionic oligomer or polymer as coagulation assistant (e) includes:
(i) a water-soluble or water-dispersible polymer comprising one or more
monomers selected from an unsaturated carboxylic acid and a derivative
thereof,
(ii) a water-soluble or water-dispersible polymer comprising an unsaturated
sulfonic acid or a derivative thereof,
(iii) a formalin condensate of a sulfonated polycyclic aromatic compound
which may contain a hydrocarbon group as a substituent, and
(iv) a mixture of two or more of (1) to (3).
The above-mentioned polymer (i) may be prepared from one or more monomers
selected from unsaturated monocarboxylic acids (e.g., acrylic acid,
methacrylic acid), dicarboxylic acids (e.g., maleic acid), alkali metal
salts thereof (e.g., sodium salts), ammonium salts thereof, and organic
amine salts thereof (e.g., triethanolamine salts). These monomers may be
used in combination with copolymerizable monomers therewith such as vinyl
acetate, isobutylene, diisobutylene, styrene, alkyl acrylates, alkyl
methacrylates, hydroxyethyl(meth)acrylate, polyoxyethylene (meth)acrylate,
(meth)acrylamide, and diaceton acrylamide.
These monomers can be polymerized or copolymerized in a conventional
manner. The proportion of the monomer components and the polymerization
degree of the polymer or copolymer to be obtained are not specifically
restricted but it is necessary that the resulting polymer or copolymer
should be water-soluble or water-dispersible.
Specific examples of the polymer (i) include acrylic acid polymer,
methacrylic acid copolymer, acrylic acid/methacrylic acid copolymer,
acrylic acid/polyoxyethylene methacrylic ester copolymer, acrylic
acid/methyl acrylate copolymer, acrylic acid/vinyl acetate copolymer,
acrylic acid/maleic acid copolymer, maleic acid/isobutylene copolymer,
maleic acid/styrene copolymer, and alkali metal, ammonia and organic amine
salts thereof. These polymers and copolymers may be used alone or in
combination of two or more of them.
Examples of the above-mentioned polymer (2) include those prepared by
polymerizing the unsaturated sulfonic acid, such as styrenesulfonic acid,
2-acrylamide-2-methylpropanesulfonic acid, vinylsulfonic acid,
methacrylsulfonic acid, acrylsulfonic acid and the like, or by
copolymerizing the unsaturated sulfonic acid with another monomer, such as
hydrophobic monomers (e.g., alkyl acrylate, alkyl methacrylate, vinyl
alkyl ether, vinyl acetate, ethylene, propylene, butylene, butadiene,
diisobutylene, vinyl chloride, vinylidene chloride, acrylonitrile, and
styrene), hydrophilic monomers (e.g., acrylic acid, methacrylic acid,
maleic acid, fumaric acid, maleic anhydride, vinyl alcohol, acrylamide,
methacrylamide, diacetoneacrylamide, N-vinyl-pyrrolidone,
2-acrylamide-2-methylpropanesulfonic acid, methallylsulfonic acid,
xylenesulfonic acid, and naphthalenesulfonic acid). Among them, polymers
and copolymers of a styrenesulfonic acid salt are more preferred.
The polymer of a styrenesulfonic acid salt may be prepared by polymerizing
a styrenesulfonic acid salt or sulfonating a polystyrene. The polymer of
styrenesulfonic acid salt has a structure represented by the following
formula:
##STR1##
The molecular weight of the polymer of a styrenesulfonic acid salt is
preferably from 1,000 or more, more preferably from 10,000 to 3,000,000.
In the above formula, M represents an alkali metal (e.g., lithium, sodium,
potassium), an ammonium group, an alkylamine or an alkanolamine.
The copolymer of a styrenesulfonic acid salt may be prepared by
copolymerizing a styrenesulfonic acid salt with another monomer or
sulfonating a copolymer of styrene with another monomer. Preferred
examples of the copolymer include a (meth)acrylic acid-styrenesulfonic
acid copolymer. In this copolymer, the molar ratio of (meth)acrylic acid
residue and styrenesulfonic acid is preferably from 1/10 to 10/1, more
preferably from 1/3 to 7/1. The average molecular weight thereof is
preferably from 1,000 to 1,000,000, more preferably from 10,000 to
700,000. Examples of the salt of the copolymer include sodium salts,
potassium salts, ammonium salts, diethanolamine salts, triethanolamine
salts, monoisopropanolamine salts, diisopropanolamine salts,
triisopropanolamine salts, and 2-amino-2-methylpropane-1,3-diol salts. In
this instance, unneutralized portions may be remained in the copolymer so
long as they deteriorate the properties of the copolymer.
The above-mentioned condensate (iii) may be prepared by subjecting
naphthalene, alkyl-substituted benzene, alkyl-substituted naphthalene,
anthracene, alkyl-substituted anthracene, lignin, or compounds having an
aromatic ring contained in petroleum residue to sulfonating reaction in a
conventional manner, and subsequently to salt formation reaction and
formaldehyde condensation. In this instance, the polymerization degree is
preferably from 2 to 30, more preferably from 3 to 10. When the
polymerization degree is less than 2, the effect of condensation is not
fully achieved, whereas when the polymerization degree is more than 30,
the molecular weight of the polymer becomes high, which may be
disadvantageous in solubility in water, for example.
As the aromatic compound, various kinds of aromatic compounds may be used
and preferred examples thereof include lignin, xylene, toluene,
naphthalene and alkylnaphthalene wherein the alkyl moiety has from 1 to 6
carbon atoms. These aromatic compounds may be used alone or in combination
of two or more of them.
Specific examples of the condensate (iii) include formalin condensates of
petroleum sulfonic acid derivatives, lignin sulfonate acid derivatives,
naphthalene sulfonate derivatives, xylene sulfonate derivatives and
alkylbenzene sulfonate derivatives. Examples of the salt thereof include
alkali metal (e.g., sodium, potassium) salts, alkaline earth metal (e.g.,
calcium) salts, amine salts, ammonium salts and the like.
Preferred examples of coagulation assistant (e) includes a styrene-sulfonic
acid copolymer, a homo- or copolymer of acrylamide t-butylsulfonic acid, a
homo- or copolymer of a vinylsulfonate, a homo- or copolymer of a
3-sulfopropyl(meth)acrylic ester salt, a formalinnaphthalenesulonic acid
condensate, lignin sulfonic acid, a polycyclic aromatic sulfonic acid
copolymer, a homo- or copolymer of acrylic acid and maleic anhydride, and
an isobutylene- or diisobutylene-maleic anhydride copolymer.
Among coagulation assistants (a) to (e), (a), (b), (c) and (e) are
preferred and (a), (b) and (e) are further preferred.
The coagulation assistant according to the present invention is added to a
deproteinized natural rubber latex in combination with an acid.
The acids which can be used in the step (2) of the process of the present
invention as a coagulating agent include formic acid, acetic acid and,
phosphoric acid and hydrochloric acid. The acid is added to the
deproteinized natural rubber latex in such an amount to give a pH value of
not higher than 7, preferably of from 3 to 6.
The coagulation assistant according to the present invention is added to
the deproteinized natural rubber latex so as to give a concentration of
from 0.01 to 10% by weight, and preferably from 0.1 to 5% by weight, based
on the weight of the latex. If the concentration of the coagulating
assistant is less than 0.01%, sufficient effect cannot be obtained.
Concentrations exceeding 10% are only uneconomical.
Addition of the coagulation assistant may be either before or after
addition of the acid, and preferably before addition of the acid.
After addition of the acid and the coagulation assistant, the latex is
allowed to stand or stirred at room temperature to cause the rubber
particles to be coagulated and precipitate. If necessary, coagulation by
the step (2) in the process of the present invention may be effected while
heating the latex.
According to the process of the present invention, the coagulation steps
(1) and (2) may be carried out either individually or in combination
therewith.
After coagulation, the coagulated rubber particles are separated from the
mixture in a conventional manner, thoroughly washed with water and then
dried. In this instance, when the nonionic surfactant is used as the
coagulating agent, it is preferable that the temperatures of the washing
water and the rubber particles are controlled at or lower than the cloud
point of the nonionic surfactant for efficiently removing the nonionic
surfactant or other surfactants.
As stated above, the raw rubber produced in the process of the present
invention has extremely reduced contents of metal ions and surfactants as
compared with the one recovered by using a metal salt as a coagulating
agent.
The present invention will now be illustrated in greater detail with
reference to Examples, but it is to be understood that the present
invention should not be construed as being limited thereto. All the
percents and ratios shown below are by weight unless otherwise noted.
EXAMPLES 1 TO 6 AND COMPARATIVE EXAMPLES 1 AND 2
A high ammonia latex of natural rubber was treated with a protease (alkali
protease) and a surfactant (a 60:40 mixture of sodium
dodecylbenzenesulfonate and polyoxyethylene (9 mol) lauryl ether) to
prepare a deproteinized natural rubber latex showing no absorption of
polypeptide at 3280 cm.sup.-1 in the IR spectrum. One part of a 10%
aqueous solution of the nonionic surfactant shown in Table 1 below was
added to 100 parts (on a solid basis) of the resulting deproteinized
natural rubber latex (solids content: 30%) in a test tube, and the mixture
was heated in a hot water bath at 90.degree. C. for 5 minutes. The state
of coagulation after heating was evaluated with the naked eye and rated
"good" (the rubber content was coagulated) or "bad" (the rubber content
was not coagulated). The results obtained are shown in Table 1.
For control, the same deproteinized natural rubber latex as used above but
containing no coagulating agent (nonionic surfactant) was tested in the
same manner. The result obtained is also shown in Table 1.
TABLE 1
__________________________________________________________________________
Cloud
Example Point Molecular
Coagulation
No. Nonionic Surfactant
(.degree.C.)
Weight
Property
__________________________________________________________________________
1 Nonylphenol EO.sup.1) (8.1).sup.3) adduct
23 576 good
2 Nonylphenol EO(20) PO.sup.2) (14) adduct
40 1880 good
3 Bisphenol EO(75) PO(20) adduct
62 3530 good
4 Dimethylpolysiloxane EO(20) PO(8)
50 40000 good
copolymer
5 Lauryl alcohol EO(20) adduct
88 1730 good
6 Oleyl alcohol EO(9) adduct
55 610 good
Comparative
Nonylphenol EO(84) adduct
exceeding
3920 bad
Example 1 100
Comparative
Decyl alcohol EO(2) adduct
less than
247 bad
Example 2 20
Control
None -- -- bad
__________________________________________________________________________
Note:
.sup.1) EO: ethylene oxide
.sup.2) PO: propylene oxide
.sup.3) The numbers in parentheses are average mole numbers of EO or PO
added per molecule of the adduct.
It is seen from Table 1 that a nonionic surfactant having a cloud point
outside of the range of 20.degree. to 100.degree. C. and a molecular
weight of less than 300 produces no effect (Comparative Example 2) and
neither does a nonionic surfactant having a molecular weight of 300 or
more but a cloud point outside of the above range (Comparative example 1).
To the contrary, in Examples 1 to 6 nonionic surfactants whose cloud point
and molecular weight fall within the respective range according to the
present invention exhibit satisfactory effect of coagulation.
EXAMPLES 7 TO 18 AND COMPARATIVE EXAMPLE 3
A high ammonia latex of natural rubber was treated with a protease (alkali
protease) and a surfactant (a 60:40 mixture of sodium
dodecylbenzenesulfonate and polyoxyethylene (9 mol) lauryl ether) to
prepare a deproteinized latex showing no absorption of polypeptide at 3280
cm.sup.-1 in the IR spectrum. Each of the coagulation assistants shown in
Table 2 below was added thereto to give the concentration shown in Table
2, and the latex was diluted to a total solids content of 15%. To the
latex was added 20% formic acid to give a final concentration of 0.5%.
After allowing the system to stand for 24 hours, the state of coagulation
was evaluated with the naked eye and rated "good" (the rubber content was
coagulated) or "bad" (the rubber content was not coagulated). The results
obtained are shown in Table 2.
For comparison, a deproteinized latex containing 0.005% of sodium
laurylsulfate as a coagulating assistant and, as a control, a
deproteinized natural rubber latex containing no coagulating assistant
were tested in the same manner. The results obtained are also shown in
Table 2.
TABLE 2
______________________________________
Concen- Coagu-
Example tration lation
No. Coagulation Assistant
(% by weight)
Properties
______________________________________
7 Sodium laurylsulfate
1.0 good
(Emal 10 powder*.sup.1)
8 Potassium oleate
0.5 good
(FR-14*.sup.2)
9 Sodium-dodecyl-
0.5 good
benzene sulfonate
(Neopelex F-65*.sup.3)
10 Polyoxyethylene (9)
3.0 good
nonylphenyl ether
(Emulgen 909*.sup.4)
11 Polyoxyethylene (20)
5.0 good
sorbitan monooleate
(Rheodor TWO-120*.sup.5)
12 Sodium lauryl 2.0 good
phosphate
13 Hexaglycerin mono-
2.5 good
oleate (polymerization
degree: 6)
14 Polyoxyethylene (10)
3.0 good
monooleate (Emanon
4110*.sup.6)
15 Laurylglucoside
1.0 good
16 Sodium salt of for-
1.0 good
malin-naphthalene-
sulfonic acid
condensate (Demol
N*.sup.7)
(number of condensa-
tion (n) = 5)
17 Lauroyl acetobetaine
2.0 good
(Amphitol 20BS*.sup.8)
18 Polyvinyl alcohol
2.5 good
(saponification degree:
78.5-81.5 mol %)
Compa- Sodium laurylsulfate
0.005 bad
rative
Example 3
Control None -- bad
______________________________________
Note:
*.sup.1 to *.sup.8 are all trade names of Kao Corporation.
As is apparent from Tables 1 and 2, raw rubber can be produced from a
deproteinized natural rubber latex in the process of the present invention
with a high efficiency.
As described and demonstrated above, the process of the present invention
can produce raw rubber from a deproteinized natural rubber latex with a
high efficiency. Further, since the raw rubber produced in the process of
the present invention substantially does not contain metallic ions, it
does not cause problems such as reductions in physical properties due to
moisture absorption, blooming, retardation of vulcanization, and a
reduction in resistance to deterioration on aging.
While the present invention has been described in detail and with reference
to specific examples thereof, it will be apparent to one skilled in the
art that various changes and modifications can be made therein without
departing from the spirit and scope thereof.
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